1. Field of the invention
The invention relates generally to esthetic dentistry, and more particularly, to the technical means that measure the translucency of dental materials and natural teeth in order to create naturally looked dental prostheses.
2. State of the Art
Translucency is a main factor that indicates the quality of the restorative dental procedures. A common situation frequently occurs when a patient gets a well color-matched restored anterior tooth, but it looks like a nonvital shade tab. This situation happens because the practitioner was not able to determine the translucency level in teeth that were adjacent to the damaged tooth and served as references for color matching. A translucency mismatch is most crucial for an incisal part of the anterior tooth which contributes mostly to the natural appearance of the patient's teeth.
A procedure for proper color matching is performed by the visual comparison of teeth against shade guide color standards. A significant problem with the visual method is that its success depends upon the color vision of the practitioner. Moreover, even in the case of perfect color vision, the dental color matching procedure can be quite anxiety provokingfor the practitioner because color and translucency change along the tooth. In order to be normalized, standard dental color shades are classified by considering the color only in the central part of the shade tab. The variation of translucency is not included in the shade description because it will affect the visual perception of the teeth and shade tabs. As a result, for matching the incisal translucent part, the practitioner must guess which central part of the nontranslucent shade tabs looks closer to the natural translucent tooth.
The recent prior art aimed to overcome the problem associated with the visual analysis of dental translucency by applying fiber optics for illuminating the tooth and for detecting the light scattered from the same side of the tooth. The idea was to determine the translucency factor by separate illuminating of different areas of the tooth with a few light sources, as described in U.S. Pat. No. 5,798,839 or by detecting the light scattered at different distances from a single light source as described in U.S. Pat. No. 5,851,113. There is one major technical obstacle to successful clinical implementation of these techniques. It is explained below without being bound by theory.
A translucent object appears like a milky glass. The higher the translucency, the more transparent object seems. The translucency parameter may be defined as a difference between color parameters that were taken when the object was analyzed against two backings, one ideally white and another absolutely dark. Consider an absolute transparent object, such as optical glass, for instance, and use a Lab color system that is based on the use of L, a, b color parameters. If the glass is measured against the white backing, the color parameters will be L.sub.w =100, a.sub.w =0, and b.sub.w =0 which corresponds to an ideal white standard placed under the glass (reflection from the glass is neglected). When the same glass is measured against an absolutely dark backing, all color parameters will be zero, L.sub.b =a.sub.b =b.sub.b =0, because no light is transmitted at all. Therefore, the color difference will be .DELTA.L=L.sub.w -L.sub.b =100, .DELTA.a=a.sub.w -b.sub.b =0, and .DELTA.b=b.sub.w -b.sub.b =0, and thus, the transluce absolute transparent glass equals 100.
However, the foregoing prior arts are entirely based on measurement of the backscattered light. They will indicate zero signals for both types of glasses mentioned above no light is scattered back in the direction from where light came. In other words, the prior arts are not able to distinguish between transparency and darkness because absorption which is independent of scattering contributes equally to transmittance and reflection. In the case of teeth, nonsensitivity to absorption will increase the color difference due to the spectral dependence of light propagation into the enamel and dentin. As described elsewhere, different color components have different absorption and scattering parameters. This example shows that translucency of the teeth has to be measured in a direct mode, namely by measuring the light (flux F.sub.t,) that passed through the tooth and has continued in the same direction as the incoming light. If F.sub.O is the incoming flux, the translucency factor, TR, can be expressed as a ratio, TR=F.sub.t /F.sub.O.times.100.
Earlier prior art was connected to the direct measurement of tooth transmission as described in U.S. Pat. No. 4,881,811. The technique has employed an integrating sphere that touched the external surface of the tooth while the tooth was illuminated from the internal side using a flexible fiber optic. The sphere was mounted in a probe that was connected to a remote spectrophotometer. The main disadvantage of this prior art is that it measures the total transmittance of the tooth because it collects the light that is scattered at all possible angles, from 0 up to 90 degrees. Another disadvantages of this prior art was the complexity and enlarged size of the probe. These do not allow for measuring a portion of the tooth that is necessary for the restoration of natural looking teeth. In addition, this prior art is not portable because it requires a cable connection with the remote spectrophotometer.
Another prior art that can be implemented for the translucency measurement of teeth is the fiber optic transillumination (FOTI) technique used for detecting cavities. It is comprised of an illuminating fiber bundle that illuminates the tooth from a powerful polychromatic light source and receiving fiber bundle that transfers a projection of the tooth to a screen or videocamera. This prior art is very complex and non-portable as it requires a powerful light source, and cannot provide an accurate measurement of translucency because the projective image is formed mostly by light scattered from the entire body of the tooth, not from the portion of the tooth that must be analyzed.
It is, therefore, an object of the invention to provide a dental translucency analyzer that is small and portable. It is also an object of the invention to provide a dental translucency analyzer able to measure translucency in a small portion of teeth and dental materials.